It's never too early to stock up on your cold weather essentials. In addition to a cozy pair of flannel pajamas and a down (or down alternative) jacket, you won't regret adding a good pair of thermal underwear to your winter shopping list. When the air gets cold and snow starts to fall, the right base layers can keep you comfortable in any conditions.
Before you buy, know that not all thermal underwear sets are created equally. While you can find affordable options at most major retailers, the right materials and design can make all difference. Your base layers should retain body heat without leaving you itchy, scratchy, or sweaty. Look for thermals that use temperature-regulating fabrics, like wool and spandex, to stay warm without overdoing it.
Keep an eye on design, too. Most thermal underwear serves as a base layer underneath other clothing—you want tops and bottoms with clean, tight silhouettes, but aren't so restrictive they becomes uncomfortable. Keep scrolling to shop 13 of the best thermal underwear pieces from brands like SmartWool, Ibex, and more.
13 of the best thermal underwear to layer up in this winter
Best thermal underwear for women
Smartwool is a smart investment. Like all Smartwool products, these leggings (or thermal undies) are crafted from Merino wool, which is known being moisture-wicking, antimicrobial, and super comfortable. Available in black, navy, and various heather options.
What reviews say: “The instant you pull these base layers out of the package you know you’re dealing with a quality product. I work for a gear retailer so I’ve had the chance to handle many base layers and these are by far my favorite.” — Smartwool customer
Similarly, Ibex also makes premium products all made from high-quality Merino wool. These best-selling thermal undies are warm without ever being stuffy or sweaty. Throw them on under snow gear, jeans, leggings—whatever you need to layer up.
What reviews say: “Great for staying warm inside during winter and a great base layer. These natural fibers don’t retain odor like the synthetic fibers. Always a great addition to a wardrobe.” — Taunya M., Ibex customer
For just $30, snag this best-selling thermal underwear set off Amazon and stay snuggly all winter long. Instead of wool, these are made from a lightweight poly-spandex blend that’s still warm enough to keep body heat where it belongs. They’re also fleece-lined for added warmth.
What reviews say: “Bought a set of these thermals in each color for my trip to Alaska over the Thanksgiving holiday… At -14 degrees they kept me warm and they are super soft and comfortable.” — Amazon customer
Breathable but still tight-knit, these thermal bottoms from Patagonia are made with spandex for better movement and flexibility. Between the flat seams, stretchy waistband, and supple fabric, they’re comfortable and get the job done when the temperature falls.
What reviews say: “I have just purchased my third pair. They are light in weight but provide great warmth in the cold. I spend a lot of time hiking, snowshoeing, and cross country skiing.” — Irene, Patagonia customer
When you want warmth without the bulk, layer on these Merino wool boxers from Stoic. The stretchy, flat seaming won’t ever dig or chafe. Great for cold weather workouts and gym sessions when shorts alone won’t cut it. Available in black and grey.
What reviews say: “These are perfect wicking underwear for hiking and camping. My second time purchasing them.” — Amazon customer
Arguably the prettiest thermal underwear on this list, these thermal leggings from Sweat Betty are just as functional as they are fashionable. They’re seamless and sweat-proof, made from dreamy Merino wool that’ll keep you cozy on the slopes and beyond. Available in black and white.
What reviews say: “These leggings are beautiful. The Merino fabric is amazing. I have a few pairs of Sweaty Betty base layer leggings that I wear as winter running tights. They are perfect.” — Sweaty Betty customer
These thermal bottoms are made from 100 percent filament silk that fit seamlessly underneath any kind of outerwear. They’re also thermoregulating, so you’ll never overheat, and UPF 50 for added protection. Available in black, grey, white, and pink.
What reviews say: “I use this and a matching top to sleep in when I am out backpacking in the back country. Warm or cool, these are perfect for staying comfortable at night.” — Amazon customer
Best thermal underwear for men
Icebreaker is another premium purveyor of all-things thermal. Its line of Merino wool base layers are versatile and reliable, guaranteed to do their job no matter where you roam.
What reviews say: “This was everything I was expecting and I am so glad I bought two pairs! Perfect winter gear for living in the cold city or hiking in the high country.” — Icebreaker customer
Kora products are made from Merino and yak wool, making them ridiculously warm in even the coldest climates. These full-length pants fit smoothly under bibs, snow pants, and more, making them perfect for just about any winter activity.
What reviews say: “This is the second item we have tested from Kora and we are impressed. If you appreciate natural materials and want a very high performing base layer, then look into yak wool!” — Engearment review
This all-season base layer is great for everyday wear, in and out of the gym. The brushed grid interior traps air, maintaining an even (but warm) body temperature as you work up a sweat. Excellent for adding heat but never bulk.
What reviews say: “Since my passion always takes me outdoors, winter time is my favorite time of the year. The cold gear base layer has never disappointed me. It is fantastic in the cold weather whether I’m skiing, snowshoeing or even snowmobiling.” — Under Armour customer
This top-selling thermal underwear set has more than 5,000 reviews on Amazon and is less than $20. It’s made of a cotton-poly blend that’s snug but never stiff or uncomfortable. A great, budget-friendly option for quality thermals.
What reviews say: “Love these thermals. Great quality for the price and I love how vibrant the red is even after several washes. Keeps me perfectly warm in a NY winter without being too uncomfortably heavy when transitioning from outside to indoors.” — Amazon customer
This luxurious thermal set is made from all natural materials that are biodegradable, making them the eco-friendliest option on this list. Both the top and bottoms are soft and stretchy, made of a thin-yet-durable fabric designed to keep you cozy while you wear.
What reviews say: “Outstanding in feel, quality, and warmth! Hate having to take them off!” — Kip H., Tani customer
The number one men’s best-selling thermals are just $35, affordable enough to snag a set in every color. The poly-spandex blend wicks moisture and sweat, keeping you dry and cool when you get moving.
What reviews say: “These long johns are thin enough, very comfy, and close fitting around the wrists, ankles and waist. Wearing them under daily clothes during winter is very practical.” — Amazon customer
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